Radio Access Networks (RAN) are normally dimensioned for daily or weekly average traffic but rarely for peak traffic conditions. Based on this dimensioning, users are able to access network resources in order to establish and release their communications.
When unexpected peak traffic situations occur (e.g. in case of emergency situations like earthquake, terrorist attacks, etc.) the mobile network can become so congested that accessibility is not possible to the great majority of users.
Similar peak traffic can also occur in special events, like concerts, sport games (football, races) or similar situations in which a huge amount of people get together; and in these cases, although operators increase as much as possible the available network resources, it is not possible to design the system in order to guarantee the normal level of accessibility.
Special users like police, ambulance services, fire brigades, and special allowed staff must be able to access the network.
However, there is currently no automatic solution to cope with the problems.
The present invention automatically detects the accessibility problems caused by unexpected high traffic load and react to the situation in order to guarantee the proper accessibility to special pre-defined high priority users (user prioritization based access control).
Besides, the present invention automatically protects the excessive load by ensuring that its workload is kept lower than a pre-configurable load level able to guarantee a correct functioning of the RNC (Radio Network Controller) and Node B machine.
The invention automatically detects the accessibility problems caused by the extremely high load, reduces overload situations (e.g. signalling, CPU usage) on the network elements, automatically guarantees accessibility in emergency situations to the emergency user (e.g. rescue services, police, etc.) and measures the effectiveness of its countermeasures and adapts its behaviour to the new traffic situation as the time goes by.
The present invention acts upon two scenarios:                1. To react to the situation in order to guarantee the proper accessibility to special pre-defined high priority users (user prioritisation based access control)        2. To be able to self protect by the excessive load by ensuring that its workload is kept lower than a pre-configurable load level able to guarantee a correct functioning of the RNC and Node B machines.        
In the present solution the availability of the 3GPP-defined resources for 3G system accessibility (RACH slots and signatures) is dynamically increased/decreased based on the level of system congestion (RRC and RAB allocation success rate) as well as on the detected congestion on the accessibility channels.
It is well-known that abbreviations and acronyms are frequently used in the mobile telephony field. Below is a glossary of acronyms/terms used throughout the present specification:    3GPP The 3rd Generation Partnership Project    AC Access Class    ASC Access Service Class    FDD Frequency Division Duplex    PLMN Public Land Mobile Network    PRACH Physical Random Access Channel    RAB Radio Access Bearer    RACH Random Access Channel    RAN Radio Access Network    RNC Radio Network Controller    RRC Radio Resource Control    TDD Time Division Duplex    UE User Equipment    SIM Subscriber Identity Module    U/SIM UMTS Subscriber Identity Module    UMTS Universal Mobile Telecommunications System